Surgical procedures, such as minimally-invasive procedures, may require a surgeon to insert surgical tools inside the body of the patient to a particular depth to reach the target area inside the patient's body. For example, minimally invasive spinal surgical procedures have been used for stabilization of vertebral bones and spinal joints and for relieving of pressure applied to the spinal nerves. Such procedures may utilize relatively small incisions and insertion of tubular retractors and cannulas while minimizing damage to muscles and other surrounding anatomical features. Minimally invasive surgical approaches can be faster, safer and require less recovery time than conventional open surgeries. There is a continuing need for improvement to the safety and speed of surgical procedures, such as minimally-invasive surgical procedures.